62 GENERAL ANATOMICAL CHARACTERS 
The essentially bipartite character of the organ and its uniformity 
of construction throughout the class are thus not lost sight of, even 
in the most complex forms. The left segment of the liver is rarely 
complicated to any further extent, except in some cases by minor 
or secondary fissures marking off small lobules, generally inconstant 
and irregular, and never worthy of any special designation. On 
the other hand, the right segment is usually more complex. The 
gall-bladder, when present, is always attached to the under surface 
of the right central lobe, sometimes merely applied to it, in other 
cases deeply embedded in its substance. In many instances the 
fossa in which it is sunk is continued to the free margin of the 
liver as an indent, or even a tolerably deep fissure (cf). The 
portal fissure (p), through which the portal vein and hepatic artery 
enter and the bile-duct emerges from the liver, crosses the right 
central lobe transversely, near the attached border of the liver. 
The right lateral lobe always has the great vena cava (vc) either 
grooving its surface or tunnelling through its substance near the 
inner or left end of its attached border ; and a prolongation of this 
lobe to the left, between the vein and the portal fissure, sometimes 
forming a mere flat track of hepatic substance, but more often 
a prominent tongue-shaped process, is the so-called “Spigelian lobe” 
(s). From the under surface of the right lateral lobe a portion is 
generally partially detached by a fissure, and called the “caudate 
lobe” (c). In Man this lobe is almost obsolete, but in most 
mammals it is of considerable magnitude, and has very constant 
and characteristic relations. It is connected by an isthmus at the 
left (narrowest or attached) end to the Spigelian lobe, behind which 
isthmus the vena cava is always in relation to it, channelling 
through or grooving its surface. It generally has a pointed apex, 
and is deeply hollowed to receive the right kidney, to the upper 
and inner side of which it is applied. 
Considerations derived from the comparatively small and simple 
condition of the liver of the Ungulata, compared with its large 
size and complex form in the Carnivora, have led to the perhaps 
too hasty generalisation that the first type is related to a herbivorous 
and the latter to a carnivorous diet. The exceptions to such a 
proposition are very numerous. The fact of the great difference 
between the liver of the Cetacea and that of the Seals cannot 
be accounted for by difference of habits of life, though it perhaps 
may be by difference of origin. 
? For further details of these modifications, see Flower’s “Lectures on the 
Comparative Anatomy of the Organs of Digestion of the Mammalia,” Medical 
Times and Gazette, Feb.-Dec. 1872. 
